Now that we know how to solve for the total number of signals in a proton NMR, it's time to move on to our second piece of information. And that's gonna be the chemical shifts of each signal. So the chemical shift indicates the exact electrochemical environment that each Proton is experiencing. Okay, now, I know that sounds kind of complicated, but there is a nice generalization we can make. What we say is that electro negative groups remember Electra negative. Just something that likes to pull electrons away will pull the electrons away from the nuclei d shielding them, making them or nay, kids, they're gonna experience the anymore more. Okay, so the shifts, the chemical shifts are going to increase or move downfield. The number will get bigger as the protons become more d shielded. Okay, Now, before we get into, like, some very specific free, some very specific shifts that you need to know, we're just gonna look like a general trend, okay? And as a general trend, what you're going to see is that as our functional groups get more and more Electra negative, the bigger than numbers get. Now, remember, all of this is in reference to T m s, which is our reference molecule that has a by definition shift of zero, because that is our reference point. Okay, so now we're seeing all of these things in order they get more and more d shielded as you go down the list. What we see is that Al Keynes cases just al cane are actually the most shielded organic molecules because there's no Electra negative things pulling electrons away. Okay, It's very, very shielded. Cesaire gonna shift at the lowest number around 1 to 2. Okay, then we have triple bonds. Triple bonds were going to come next. That's all kinds. Okay, All kinds are gonna come next. About 2.5 still relatively shielded. Okay, then we have this very broad, um, group called Z ch. Now, what does e stand for Z is just gonna be something Electra Negative. That's next to it. Okay. So Z could stand for an atom. It could stand for a group. That is a lecture. Negative. I'm just putting e n for something. A lecture. Negative. Now, this has a range anywhere from 2 to 4. Because it really depends on what that Z is. If it's something super election, negative flooring. Then it's going to close to a full or four if it's something less election negative than a little bit less right then we've got alcohol and a mean now these have a very broad range of 1 to 5. Okay? And there's so such a broad range, in fact, that I consider these useless in terms of chemical shift because it's so variable that the difference between one through five is really huge on NMR. Remember, I told you the NMR really only goes like 13 so one through five is like a third of the entire spectrum. Okay, that being said, it's not very helpful. If I have a peek at two or if I have a peek at five, it doesn't tell me much because I don't really know what it is. So I'm really just gonna not even focus on those shifts because they're pointless because they're so wide okay, they don't really give us a lot of information. Okay, then we have Al Keene's, which results higher than the two other hydrocarbons at 4.5 to 6. Now, I'm not gonna be able to get into the theory of why Al Keane's are higher than all kinds. But just know that it actually has to do with a very technical explanation. Dealing with Molecular Orbital's and the shapes of the molecular orbital's around the double bond Well, actually d shield the hydrogen more than the shapes of the orbital's on a triple bond. So that's why. Okay, if you're really interested, Wikipedia it, right? So benzene Ben zines are getting more d shielded if you think about it. Benzine has a lot of electrons inside. It's got those three triple bonds, the clutch logo, right? So there's a lot of electrons and there is pulling electrons kind of towards itself. So benzene is going to be higher 68. And now this is where things start to get really d shielded alga hide and carb oxalic acid. One thing they have in common is that both of those h is I'm just going to draw the car broke cilic acid there next to carbon eels. Now, remember, a carbon eel has a very strong die poll pulling away from it. On top of that car back Selic acid has another strong dipole with the oxygen pulling away from it all. That's to say that Well, I didn't actually mean to draw. Exactly. They're I meant to draw it here that the oxygen is pulling electrons away from the age. All that is to say that carve oxalic acids and Alba hides are gonna have the most D shielded or the most naked protons. Because you can imagine that basically, this hydrogen here doesn't have any electrons around it because all the electrons are getting sucked up by the Carbonell sucked up by the oxygen. Something is like butt naked. Okay. And that's gonna our highest peak possibles. Car oxalic acid at 13. Okay, Now, the specific chemical shifts that you need to know for your class for your specific classroom is really gonna be up to your professor. There is absolutely no way for me to know on my end exactly what shifts your professor thinks is important and which ones they say you don't need to worry about. In fact, double check. Your professor might even give you a sheet on your exam. That has all these shifts already written out for you. So you don't have to memorize them. It all okay, but as always, I'm going to go over them just in case, okay? And honestly, even if your professor told you don't need to memorize these shifts, I still would recommend watching this part of the video because this can help you a lot when we do structure termination later on in this course. Okay, so let's go ahead and just go through some more specific ranges. Okay? So first of all, we're just going to start at the bottom. Remember that our bottom is TMS. Okay, Now, we talked about Al Keynes being and the 1 to 2 range, and it turns out that Al Keynes actually follow a pattern that the more substituted the Al Cain. The more our groups it has, the higher it's going to result. Okay, so that means that your professor may want you to be able to tell the difference between a primary al cane and a tertiary, and typically, like a tertiary, one could come out like at 1.8, whereas a primary one might come out like at 1.1 C. So it's It's like a little differences here and there. And then, you know, a secondary would be somewhere in the middle like 1.4. Okay, All of these ranges are definitely variable. Um, it doesn't have to be exactly that, but I'm just trying to illustrate how, as you move towards tertiary, you actually get a little bit more D shielded. Okay, Now we move on to our ZC z C H range, in which we said that it's anywhere between two and four, and it really depends on what Z is. Okay, well, that's actually really important. We have to learn some specific Z's here on. I want you to know these. So first of all, the most Electra negative things that we can put next to a a car next to a hydrogen are either flooring or oxygen. Both of these guys are actually going to result in a peak of just about four. Okay, so if you ever see on like, an O. C. H. That's common like an ether that usually results right around 43. etcetera. Okay, the next one I want you to be aware of is kind of the middle ground, which is nitrogen, and I a dying. Okay, Now, if you think about it, think about your periodic table in terms of election to get 70 goes af c l br I write. So your election negativity goes up as you get closer to flooring. So that means that I would expect that iodine would be the least shifted, um, alcohol. Hey, live. And that's exactly the case. Iodine and nitrogen come out about three with the other alcohol highlights. As you can see, b r and C l coming out somewhere in between. So we could theorize it's something like 3.2 and 3.5, you know, just something in the middle. Okay, not for you to memorize, just for you guys to grasp and understand the general picture. Okay, Now, this part is actually the most important part in terms of I think in terms of your long term knowledge, some Z's additional z's that we like Thio talk about our benzene rings, carbon eels and a little groups. Okay. And these are groups that are gonna be ableto pull electrons towards themselves. Okay, Now I put that they're all roughly around two. So if you just wanted to remember that they're all about to that's fine, but they do kind of going order. So for example, of benzene will typically be around 2.3, whereas a carbon eel will usually be around to one where, as an ally will usually be about 1.9. Okay, so they're all in the range of two. But there is kind of a hierarchy of benzene and carbon Neil being higher than a little. Okay, so just keep in mind that really It depends on what the Z is is going to tell you where it's on this 2 to 4 spectrum. Okay, um, now going down to the triple bond triple bond results anywhere from, like 2.5 to 3. Okay, so that whole range is kind of fair game for the triple wand. What we have for the double bond thes rangers are really just the same as the same as the one I stated before. 4.5 to 6 for a double bond for a benzene ring. Anywhere from 6 to 8 for Aldo. Hide anywhere from 9 to 10. And for bent for carb oxalic acid anywhere from 10 13. Okay. Um, so there you have it. Okay. So, really, all I did in this section was I went more into depth on the Z portion and more into depth on the alcohol on the alcohol version because of the fact that it really kind of depends on the types of disease you have or the types of alcohol groups you have. All right. Awesome. One last thing. I had the alcohols and amines at the bottom. This just gives you a visual of how large that swath is and how really useless it is. We don't really use this part of the graph. We don't really worry about it because it doesn't tell us much information. Okay, so now we're gonna do a practice problem. What I want you guys to do is use the definitions like an open book exam. Thio, look at this molecule and tell me what you think the ranking would be in terms of shielded to D shielded. It says, order the falling five protons in order from most the shield, it's that means highest number to most shielded. So that means to lowest number, right? So go ahead and started the highest parts per million, the highest chemical shift. And then we can go ahead and work our way down to the lowest one. Just order the protons the way you see fit. And then I'll answer the question
Ranking Shielded Protons
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So first, I'm just gonna go over the rankings in order. And then I'll go over each individual chemical shift just to reinforce what we just learned. So our highest number are most d shielded is gonna be h five. Okay, because H five is on a double bond, so that has the highest range, as you can see above. Okay, so it's going to go from age five, then what's the one with the next highest number? Okay, that's actually going to be hte too, because H two is directly attached to a carbon that has flooring the most electro negative Adam on it. So that would be an example of Z C h. Okay, someone's going to come in next. So H five was double bond. H two is the CH. Okay, so then after that, what I'm going to get is h three, okay, Because H three is on a triple bond. And remember that triple bonds results a little bit lower than a flooring would result. Then we would get is a judge. Four, because if you notice h four is actually a Well, okay, so this would be an example of Z c. H. But It's a little OK, now I'm just gonna erase this and move it up a little bit. Z c h Now a lil is actually on the lower side of the C H. But it still counts. Okay, so that's alot. And then finally we would end up with H one at the bottom because it's nothing. All it is is just c h. It's just a al cane. Okay, so hopefully that makes sense so far. Now, let's go over the exact chemical shifts. Now something that I neglected to mention in the previous example when I showed you guys spectrum is that chemical shifts are actually denoted by a Greek symbol. And this Greek symbol is the lower case Delta. Okay, so lower case Delta is the same thing as saying parts per million. Okay, so I'm just gonna put all of the different parts per million here. Okay, What I would expect for H five is that it's somewhere between 4.5 and six will just give it a shift of five. Okay. What we would expect for H two is that it's on the top range of Z ch. Because there's a flooring president. So I'm going to say that one's four around four than for age three. Um, since it's on a triple bond, it's somewhere between 2.5 and three. We'll just give it a chemical shift of three. Make it easy. Okay, Now for H four, because it's a lil. This is gonna be around to remember I said that. Usually they're a little bit below two. So you know what? Even though I could make it easy, I could say to I'm just gonna be a little more accurate. I'll say that it's like 1.9, because usually it's right below two. Okay. And then finally, we have h one, which it's secondary. So it's actually probably not gonna be 1.0. It's probably gonna be a little bit more in the middle. Probably something a little more like 1.4. Okay, so I got a little bit tricky at the end. Sorry if I'm blocking that a little bit. I'm not trying to trying to trick you guys or anything. Just trying to show you guys kind of the way. This works the general trend. Um, and that a lot of times you are going to see a little fluctuations with these values. And the biggest point isn't to argue over 3.94 to memorize and understand kind of the general idea of what's going on. Okay, One more note about this, um, you know, these values that I taught you, it might be in your best interest toe. Learn these values because the sheet that you get on your exam in case your professors just giving you these shifts, right? There's some professors that really don't care for you to memorize. They just give them to you. You might not understand them the same way that you understand them here, the sheet that you get. Okay, so sometimes it's just better to learn it anyway. And then you can go into your exam more confident. Okay, so I'll leave that one up to you guys. But anyway, um, that being said, let's go ahead and move onto the next topic.
Which of the labeled hydrogens will be most de-shielded?
Which compound possesses a hydrogen with the highest chemical shift for its 1H NMR signal?